1. Field of the Invention
This invention relates to the preheating of a heat load liquid which is to be fed to an evaporator, before it is heated in the evaporator, and the invention is applicable, not in a restrictive sense, to the preheating of an organic working fluid, such as flon used in a flon turbine generating system. The term flon refers to those known as Freon (a trademark).
2. Related Art
An evaporator is used to heat a liquid for changing it into vapor, by subjecting the liquid to heat exchange with a heating medium to cause it to take latent heat for evaporation away from the heating medium. A preheater is used to obtain higher temperature vapor by using the same heating medium. A flon turbine generating system will now be described by way of example.
A flon turbine generating system is a heat recovery system having the Rankine cycle applied thereto, an example of which is described in Japanese Patent Application Laid-Open Specification No. 60-144594. It comprises an evaporator for evaporating flon, which is a working fluid, by heating it with industrial wastewater used as a heat source, a vapor prime mover, or vapor engine, adapted to be driven for rotation by the high temperature and high pressure flon vapor produced by the evaporator, a condenser for cooling and condensing the flon vapor reduced in pressure as it has done work, and a flon circulating pump for feeding liquefied flon back to the evaporator; these components are connected together in a closed loop, and the output shaft of the vapor prime mover is connected to an electric generator.
The function of the evaporator is to evaporate liquid phase flon and cause the latter to take latent heat away from the heating medium, so as to provide high temperature high pressure flon vapor. And the higher the flon vapor temperature, the greater the output of the system. Thus, to provide a higher output by using the same heat source, it is contemplated to increase the vaporization temperature in the evaporator by preheating flon liquid.
However, since the heat conductivity of flon or the like used as this kind of working fluid is as low as about 1/10 of that of water, the coefficient of overall heat transmission obtained will be low if a conventional evaporator is used and even if a plate type heat exchanger, which is said to be highly effective, is used, only 500 kcal/m.sup.2 H.degree. C. or thereabouts will be obtained at the most. Therefore, to attain the sufficient preheating effect, it is necessary to use a large-sized preheater, which is high in cost and requires much space; thus, practical use of such large-sized preheater has been difficult.